U.S. patent number 5,449,352 [Application Number 08/210,997] was granted by the patent office on 1995-09-12 for topsheet for use in disposable body fluid absorptive articles.
This patent grant is currently assigned to Mitsui Petrochemical Industries, Ltd., Uni-Charm Corporation. Invention is credited to Takamitsu Igaue, Tsutomu Kido, Shigeyuki Motomura, Kazunari Nishino, Shizuo Shimizu, Hisashi Takai.
United States Patent |
5,449,352 |
Nishino , et al. |
September 12, 1995 |
Topsheet for use in disposable body fluid absorptive articles
Abstract
A topsheet for use in body fluid absorptive articles is so
improved that collapse and clogging of liquid passages therein may
be reliably avoided. The topsheet includes an upper sheet, provided
with skin-contacting areas and liquid passages, and a lower sheet
provided with skin-non-contacting areas, areas welded to the liquid
passages, and exposed areas. The exposed areas are welded to each
of the liquid passages around lower openings thereof so as to
protect the liquid passage against collapse and clogging. The
exposed areas define a skin-contacting surface which rises up into
each of the liquid passages without extending above the upper
surface of the skin-contacting areas. The upper sheet cooperates
with the lower sheet to define cavities extending in the direction
of the topsheet thickness.
Inventors: |
Nishino; Kazunari (Ohtake,
JP), Motomura; Shigeyuki (Yamaguchi, JP),
Shimizu; Shizuo (Tokyo, JP), Igaue; Takamitsu
(Kawanoe, JP), Kido; Tsutomu (Kawanoe, JP),
Takai; Hisashi (Kawanoe, JP) |
Assignee: |
Mitsui Petrochemical Industries,
Ltd. (Tokyo, JP)
Uni-Charm Corporation (Ehime, JP)
|
Family
ID: |
13961503 |
Appl.
No.: |
08/210,997 |
Filed: |
March 21, 1994 |
Foreign Application Priority Data
|
|
|
|
|
Mar 24, 1993 [JP] |
|
|
5-089101 |
|
Current U.S.
Class: |
604/383; 604/358;
604/366; 604/370; 604/375; 604/378; 604/385.01 |
Current CPC
Class: |
A61F
13/15731 (20130101); A61F 13/15739 (20130101); A61F
13/512 (20130101); A61F 13/5123 (20130101); A61F
13/5116 (20130101); A61F 2013/15447 (20130101); A61F
2013/15967 (20130101); A61F 2013/15991 (20130101); A61F
2013/51078 (20130101); A61F 2013/51165 (20130101); A61F
2013/51173 (20130101); A61F 2013/51178 (20130101); A61F
2013/51182 (20130101); A61F 2013/5127 (20130101); Y10T
428/24331 (20150115) |
Current International
Class: |
A61F
13/15 (20060101); A61F 013/15 (); A61F
013/20 () |
Field of
Search: |
;604/358,366-367,370,375,378-385.1 ;602/43-47 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Green; Randall L.
Assistant Examiner: Zuttarelli; P.
Attorney, Agent or Firm: Lowe, Price, LeBlanc &
Becker
Claims
What is claimed is:
1. A topsheet for use in body fluid absorptive articles,
comprising:
(1) a first sheet made of thermoplastic film and a second sheet
made of nonwoven fabric of thermoplastic fibers,
(2) said first sheet being provided with a plurality of liquid
passages each extending through said topsheet from tan upper
opening to a lower opening of said passage, and a skin-contacting
area continuously formed around said upper openings,
(3) said second sheet underlying said first sheet and provided with
a skin-non-contacting area opposed to said skin-contacting area,
areas welded to said liquid passages along peripheral edges of said
lower openings, and exposed areas within said liquid passages, each
of said exposed areas having a side wall and an apex rising up into
each of said liquid passages without extending above an upper
surface of said skin-contacting area, and
(4) there are defined cavities between side walls of said liquid
passages, and said skin-non-contacting area is spaced by said
liquid passages from said skin-contacting area.
2. A topsheet according to claim 1, wherein said first sheet is
hydrophobic and said second sheet is hydrophilic.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a liquid-permeable topsheet for
use in disposable body fluid absorptive articles such as sanitary
napkins, disposable diapers and training pants.
In liquid-permeable topsheets used for body fluid absorptive
articles, a technique is well known to make the topsheet from
plastic film or nonwoven fabric, and to provide it with liquid
passages each extending from top to bottom thereof. The upper
surface of the sheet is in contact with the wearer's skin, lower
openings of the respective liquid passages are in contact with an
absorbent core so that capillary action occurring within each
liquid passage may be utilized to transfer excreted body fluids
toward the absorbent core.
Japanese Patent Publication No. 1982-17081 discloses a technique
wherein a topsheet made of polyethylene film is provided with
conically tapered capillaries having lower ends capillaries are
arranged to be in close contact with an absorbent core.
According to a technique disclosed by Japanese patent application
Disclosure No. 1985-259261, a topsheet made of plastic film is
provided with cylindrical liquid passages with their lower ends
extending into an absorbent core. Such cylindrical liquid passages
are more stable and therefore less deformable than conical liquid
passages under a large load in the axial direction.
Japanese patent application Disclosure No. 1992-152945 discloses a
technique according to which there is provided a high density area
or rib continuously surrounding lower openings of respective liquid
passages. This technique certainly stabilizes an opening of each
liquid passage against deformation as well as collapse and allows
the body fluids to be effectively transferred toward an absorbent
core.
U.S. Pat. No. 4,741,941 discloses a method for making a topsheet
provided with liquid passage utilizing the manufacturing process
for melt blown nonwoven fabric or span bond nonwoven fabric. It is
also proposed by this patent that woody pulp is fed onto the lower
side of the topsheet and a combination thus integrated is used for
absorptive articles.
Japanese patent application Disclosure No. 1981-11058 discloses a
technique according to which an upper sheet made of hydrophobic
material is integrally combined with a lower sheet made of
hydrophilic material so that the lower sheet partially rises up
through a layer of the upper sheet until it is exposed beyond the
upper surface of the upper sheet and thereby a plurality of
liquid-permeable spots are formed. According to this technique, the
aforesaid liquid passages may be replaced by these liquid-permeable
spots to introduce the body fluids toward an absorbent core.
The soft touch is generally essential to the topsheet and the
conventional topsheets as disclosed by the above-identified Patent
Publication and Disclosure are also made of thin and soft materials
from such a viewpoint. With a negative consequence, however, the
conical liquid passages disclosed by the Japanese Patent
Publication No. 1982-17081 as well as the cylindrical liquid
passages disclosed by the Japanese patent application Disclosure
No. 1985-259261 are disadvantageous in that the lower openings,
i.e., free ends of these liquid passages are liable to be deformed,
so that liquid passages readily collapse, for example, even under a
relatively low pressure against the wearer and the body fluids are
often prevented thereby from being smoothly transferred toward the
absorbent core. While stability of each liquid passage against a
compressive force axially exerted on the liquid passage can be more
or less improved, the liquid passage is still easily collapsed
under a force transversely exerted on the liquid passage since,
after all the liquid passage comprises soft material.
While the technique disclosed by the above-identified Japanese
patent application Disclosure No. 1992-152945 may theoretically
alleviate the problem of collapse, both a thickness of the topsheet
and a diameter of the liquid passage are unfeasibly fine, i.e.
would not be easy to provide the previously mentioned high density
area or rib continuously surrounding the lower openings of the
respective liquid passages although this is one of the most
important features of the disclosed technique.
The technique disclosed by U.S. Pat. No. 4,741,941 provides a soft
cloth-like touch by using melt-blown nonwoven fabric, however such
nonwoven fabric lacks firmness and consequently the liquid passages
are liable to collapse and clog. In addition, the nonwoven fabric
is in rather close contact with the pulp layer fed to and combined
with the lower side of the nonwoven fabric and, when this combined
material is used in the absorptive articles, a quantity of moisture
once held by the pulp layer readily exudes and spreads over the
upper surface of the melt-blown nonwoven fabric under body pressure
of the wearer who experiences a unpleasant wetness.
The technique disclosed by Japanese patent application Disclosure
No. 1981-11058 is free from apprehension that the liquid passages
might be collapsed and clogged and the lower sheet visibly exposed
through the upper sheet as viewed from above advantageously
functions to absorb sweat when it comes in contact with the skin of
the wearer, since the lower sheet is hydrophilic. However, the
quantity of moisture once held by the lower sheet readily flows
back toward the upper sheet under a body pressure of the wearer,
since the lower sheet is in close contact with the upper sheet
primarily composed of nonwoven fabric. Accordingly, this technique
also has a problem that the wearer experiences an unpleasant
wetness. In view of these unsolved prior art problems left behind
by the prior art, it is a principal object of the invention to
provide a topsheet comprising a first sheet having a
skin-contacting area and a second sheet underlying said first
sheet, wherein said first sheet is provided with liquid passages
and said second sheet is welded to said first sheet around lower
openings of the respective liquid passages so as to restrict
possibly occurring deformation of the liquid passages, on the one
hand, and spaced from the lower side of the skin-contacting area to
avoid possibly occurring backflow of body fluids from the second
sheet toward the first sheet, on the other hand, and thereby solve
the problems encountered by the conventional topsheets.
SUMMARY OF THE INVENTION
The object set forth above is achieved, according to a first aspect
of the invention, with a topsheet for use in a body fluid
absorptive articles. The topsheet includes a plurality of liquid
passages each extending through the topsheet from an upper opening
to a lower opening thereof and a skin-contacting area continuously
formed around the upper openings of the respective liquid passages.
The topsheet comprises a first sheet made of thermoplastic sheet
and provided with said liquid passages and skin-contacting area,
and a second sheet underlying said first sheet and made of nonwoven
fabric of thermoplastic fibres and provided with a
skin-noncontacting area opposed to said skin-contacting area, an
area welded to said liquid passages along peripheral edges of their
lower openings and an area exposed within said liquid passages so
that inner walls of said liquid passages, said skin-contacting area
and said skin-noncontacting area spaced by said liquid passages
from said skin-contacting area cooperate together to define
cavities extending in the direction of the topsheet thickness.
Preferably, said area exposed within the liquid passages defines
skin-contacting spots rising up into the respective liquid passages
but not beyond the upper surface of said skin-contacting area.
Preferably, said first sheet is hydrophobic and said second sheet
is hydrophilic.
The object set forth above is achieved, according to a second
aspect of the invention, by a method for making the topsheet for
use in body fluid absorptive articles, said topsheet being provided
with a plurality of liquid passages each extending through the
topsheet from an upper opening to a lower opening thereof and a
skin-contacting area continuously formed around the upper openings
of the respective liquid passages. The method comprises the steps
of forming the first sheet provided with said liquid passages and
said skin-contacting area from a thermoplastic sheet and blowing
molten fibres onto a lower side of said first sheet to form a
second sheet made of melt-blown nonwoven fabric, wherein said
second sheet has a skin-noncontacting area spaced from a lower
surface of the skin-contacting area defined by said first sheet and
an area welded to said liquid passages around their lower openings
and wherein said skin-contacting area, inner walls of said liquid
passages and said skin-contacting area cooperate to define cavities
extending in the direction of the topsheet thickness.
The object set forth above is achieved, according to a third aspect
of the invention, by an apparatus to make the topsheet for use in
the body fluid absorptive articles, said topsheet being provided
with a plurality of liquid passages each extending through the
topsheet from an upper opening to a lower opening thereof and a
skin-contacting area continuously formed around the upper openings
of the respective liquid passages. The apparatus comprises:
(1) at least one melt extruder exclusively to form a first sheet
provided with said liquid passages and skin-contacting area;
(2) a mold against which molten fibres are blown from said
melt-blow extruder exclusively for the formation of said first
sheet to form melt-blown nonwoven fabric, said mold being provided
with a plurality of protrusions and indents which are alternately
arranged to serve as forming dies to form said nonwoven fabric with
said liquid passages and a skin-contacting area and being
responsive to an output of molten fibres from said melt-blow
extruder exclusively used for the formation of the first sheet to
operate at the optimum speed;
(3) at least one melt-blow extruder exclusively used for the
formation of a second sheet adapted to blow molten fibres against a
lower side of said first sheet released from said mold and thereby
to form said second sheet comprising melt-blown nonwoven fabric
welded to the respective liquid passages around their lower
openings;
(4) conveyor means to transport said first sheet toward said
melt-blow extruder exclusively used for the second sheet; and
(5) suction means provided in opposition to said melt-blow
extruders respectively used to form the first sheet and the second
sheet, respectively.
With the topsheet constructed as described above, the second sheet
made of nonwoven fabric is welded to the liquid passages around
their lower openings so as to restrict the deformation possibly
occurring in peripheral edges of the respective lower openings.
Additionally, the first sheet and the second sheet are continuous
with the liquid passages around their upper and lower openings,
respectively, so as to stabilize the liquid passages reliably not
only against axial forces but against transverse forces as
well.
The body fluids flow into the liquid passages and reach the lower
openings thereof, whereupon the body fluids permeate through the
second sheet, and are then partly absorbed by spots of the
absorbent core immediately underlying these lower openings, and
partly diffuse laterally through the second sheet and are absorbed
by the portions of the absorbent core which are in contact with the
skin-noncontacting area of the second sheet. The skin-noncontacting
area of the second sheet moistened by such diffusion is kept spaced
from the lower side of the skin-contacting area and there is no
apprehension that the backflow of the body fluids from the
skin-noncontacting area toward the skin-contacting area might give
the wearer an unpleasant feeling of wetness.
The second sheet is hydrophilic and, when its skin-contacting
surface rising up into the liquid passages comes in contact with
the skin of the wearer, the capillary action occurring between the
fibres constituting this sheet functions to transfer sweat into the
absorbent core.
In the method for making the topsheet of the invention comprising
the first sheet and the second sheet, molten fibres are blown
against the lower side of the first sheet provided with the
skin-contacting area and the liquid passages to form the second
sheet made of melt-blown nonwoven fabric, and thereby the second
sheet is welded to the first sheet around the lower openings of the
respective liquid passages and the skin-noncontacting area is kept
spaced from the lower side of the skin-contacting area. The second
sheet is visibly exposed within the respective liquid passages when
the first sheet is viewed from above.
The apparatus for continuously making the topsheet of the invention
comprising the first sheet and the second sheet comprises the
melt-blow extruder exclusively used to form a first sheet, the mold
being responsive to the output of molten fibres from the melt-blow
extruder to operate at the optimum speed, the melt-blow extruder
exclusively used to form the second sheet on the lower side of the
first sheet, and conveyor means for the first sheet.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described by way of example in reference with
the accompanying drawings, in which:
FIG. 1 is a perspective view showing, as partially broken away, a
sanitary napkin;
FIG. 2 is a sectional view partially showing a topsheet in an
enlarged scale;
FIG. 3 is a schematic diagram illustrating a topsheet manufacturing
process;
FIG. 4 is a diagram similar to FIG. 3 but showing an alternative
layout of the topsheet manufacturing process;
FIG. 5 is a magnified microscopic photo showing a section of the
topsheet;
FIG. 6 is a magnified microscopic photo showing upper openings and
apices of liquid passages in the topsheet;
FIG. 7 is a magnified microscopic photo showing the upper openings
as viewed from right above; and
FIG. 8 is a magnified microscopic photo showing the liquid
passages.
PREFERRED EMBODIMENTS OF THE INVENTION
Referring to FIG. 1, a sanitary napkin 1 comprises a
liquid-permeable topsheet 2, a liquid-impermeable backsheet 3 and
an absorbent core 4 sandwiched between sheets 2, 3. Topsheet 2
entirely envelops the absorbent core 4 with opposite side edges
thereof being overlapped and sealed together on the backside of the
napkin 1 and edge portions extending along longitudinally opposite
ends of the napkin 1 being also sealed together. The backsheet 3 is
interposed between the topsheet 2 lying on the backside of the
napkin 1 and the absorbent core 4.
Referring to FIG. 2, the topsheet 2 is schematically illustrated in
a partial section cut in the direction of its thickness. As
illustrated, the absorbent core 4 is in close contact with the
underside of the topsheet 2. The topsheet 2 comprises an upper
sheet 7 in the form of nonwoven fabric which comprises, in turn, an
integral laminate of a first layer 7a and a second layer 7b both
made of melt-blown fibres, and a lower sheet 8 underlying the upper
sheet 7 and made of melt-blown nonwoven fabric. While the upper
sheet 7 is described herein as a two-layered sheet, the upper sheet
7 may be formed as the single-layered sheet comprising any one of
the first layer 7a and said second layer 7b.
The upper sheet 7 has upper openings 11 and lower openings 12. The
upper sheet 7 further includes a plurality of liquid passages 13
each extending through the sheet 7 from the upper opening 11 to the
lower opening 12 and a skin-contacting area 14 which is formed as a
continuous planar zone extending around the respective upper
openings 11. The density and/or fineness of the first layer 7a may
be selected to be higher than those of the second layer 7b to
enhance the firmness of the upper sheet 7, and to maintain the soft
touch of the second layer 7b.
The lower sheet 8 includes a skin-noncontacting area 15 opposed to
the skin-contacting area 14 of the upper sheet 7, an area 16 bonded
to peripheral edges of the lower openings 12 and an area 25 exposed
within the liquid passages 13. The upper sheet 7 and the lower
sheet 8 are integrated with each other by means of welding and/or
mechanical intertwinement around the respective lower openings 12.
An upper side 15A of the skin-noncontacting area 15 is spaced from
an underside 14B of the skin-contacting area 14, so the sheets 7, 8
cooperate with walls of the liquid passages 13 to define cavities
20. The exposed area 25 rises up into the respective liquid
passages 13 and is truncated-cone- or cone-shaped as viewed in a
section cut in the direction of the topsheet thickness. The exposed
area 25 has a side wall 17, an apex 18 and a height h approximately
equal to or smaller than a height H of the liquid passages 13.
Accordingly, the apex 18 is substantially coplanar with the
skin-contacting area 14 or slightly lower than the skin-contacting
area 14, and not only the skin-contacting area 14 but also the apex
18 come in contact with the wearer's skin under a body pressure
exerted on the skin-contacting area 14. A V-shaped groove 19 is
defined between the side wall 17 and the wall of the associated
liquid passage 13. Inside the truncated-cone-shape, i.e., between
the apex 18 and the absorbent core 4, a space 18A is defined,
within which there is little or no extending fibres of the first
sheet 7a and the absorbent core 4. The skin-noncontacting area 15
is in contact with the absorbent core 4 comprising a mixture of
fluff pulp and high absorption polymer powders.
In the topsheet 2, both the upper openings 11 and the lower
openings 12 of the respective liquid passages 13 may be selectively
configured, for example, as circular, elliptical, polygonal,
indeterminate shaped openings. For example, with the liquid
passages 13 each having upper and lower openings which are circular
shaped, it is preferred that the upper opening 11 has a diameter of
0.5 to 5 mm at an opening/area ratio of 20 to 80% and each liquid
passage 13 has a height H of 0.1 to 5 mm. The lower opening 12 may
have a diameter larger or smaller than the diameter of the upper
opening 11. The fineness of the melt-blown fibres forming the
melt-blown nonwoven fabric of the second layer 7b and the lower
sheet 8 is preferably in the order of 0.01 to 1 denier in order to
assure the soft touch but the fineness of melt-blown fibres forming
the first layer 7a may be 1 denier or higher. The topsheet 2 can
present an air-permeability so far as there are interstices among
the fibres. When such air-permeability is not required, the upper
sheet 7 as a whole may be formed by a plastic sheet rather than by
a melt-blown nonwoven fabric or only the first layer 7a may be
formed by such plastic sheet. In such a case, the surface of the
sheet may be embossed to make it rough, if necessary.
Referring to FIG. 3, a process of manufacturing the topsheet 2 is
schematically illustrated. The process comprises a first molding
step 28 utilizing a molding drum 30 and first and second melt-blow
extruders 31, 32 provided around the molding drum 30 and a second
molding step 29 utilizing an endless belt 33 and a third melt-blow
extruder 34 provided above the endless belt 33. It should be
understood that, when it is desired to form the first sheet 7 as
the single-layered sheet, any one of the first and second melt-blow
extruders 31, 32 may be suspended.
In the first process 28, the molding drum 30 is provided around its
outer peripheral surface with protrusions 35 and indents 36 which
are alternately arranged and serve as forming dies so that
melt-blown fibres 40 are blown from the first melt-blow extruder 31
against the forming dies under the effect of sections 41 to form a
nonwoven fabric layer 40a destined to be the first layer 7a of the
first sheet 7. Similarly, melt-blown fibres 42 are blown from the
second melt-blow extruder 32 against the nonwoven fabric layer 40a
to form a nonwoven fabric layer 42a destined to be the second layer
7b of the first sheet 7. A laminate of these nonwoven fabric layers
40a, 42a is then molded by the drum 30 to obtain a roll 7A of the
first sheet 7 having skin-contacting area 14 formed by the
protrusions 35 and the liquid passages 13 formed by the indents 36.
It should be understood that various factors such as respective
amounts of the fibres 40, 42 to be blown, the intensity of
respective sections 41 and the depth of each indent 36 may be
adjusted during the first molding process 28 so that the fibres 40,
42 may extend upward along side walls of the respective indents 36
so as to form the liquid passages 13 and may get loose at bottoms
of the respective indents 36 so as to form openings 37 destined to
be the lower openings 12 of the first sheet 7. Inner and outer
surfaces of the molding drum 30 are air-permeable.
The roll 7A is separated from the peripheral surface of the molding
drum 30 as it is transferred from the first molding process 28 to
the second molding process 29, and laid on the endless belt 33 with
its surface which has contacted the peripheral surface of the
molding drum 30 facing upward. Under the effect of suction 43,
melt-blown fibres 44 are blown from the third melt-blow extruder 34
against the surface facing upward to form a nonwoven fabric layer
44a destined to be the second sheet 8. The amount of the fibres 44a
to be blown and the intensity of the suction 43 may be adjusted to
assure that the fibres 44 are exposed at the openings 37, extending
upward into the liquid passages 13 and, if it is necessary, the
forward end of the melt-blown nonwoven fabric layer 44a may come in
contact with the upper surface of the endless belt 33 to form a
planar layer defining the apex 18 as well as the space 18A of the
lower sheet 8. It should be understood that the effect of the
suction 43 may be attenuated to reduce or practically eliminate the
rise-up of the melt-blown nonwoven fabric and such product also may
be used as the topsheet 2.
FIG. 4 illustrates an alternative process for manufacturing the
topsheet 2 which is somewhat different from the process illustrated
by FIG. 3. Referring to FIG. 4, molding drum 30 is replaced by an
endless belt 61 provided with the protrusions 35 and the indents 36
which are alternately arranged and serve as forming dies to form
the melt-blown nonwoven fabrics 40a, 42a and the endless belt 61 is
counterclockwise rotated by driving rolls 62, 63. The remainder of
this process is substantially similar to that illustrated by FIG.
3. When the first and second melt-blow extruders 31, 32 are too
large to install them at closely adjacent locations, it will be
convenient to employ this endless belt 61.
In both processes illustrated by FIGS. 3 and 4, the melt-blown
fibres 40, 42 forming the first or upper sheet 7 are fluffed around
the lower openings 12 in the direction of the suction 41. The
melt-blown fibres 44 blown from the third melt-blow extruder 34
against this upper sheet 7 are welded to and/or twist about the
other melt-blown fibres 40, 42 and thereby integrate the second or
lower sheet 8 with the upper sheet 7. In both processes
illustrated, the lower layer 40a of melt-blown nonwoven fabric
having a higher density or fineness is first formed in order to
make the topsheet 2 firm and then the upper layer 42a of melt-blown
nonwoven fabric having a lower density or fineness is formed in
order to provide the topsheet 2 which can give its wearer a
cloth-like soft touch.
FIGS. 5 through 8 are magnified microscopic photos of the topsheet
2 produced by the process illustrated by FIG. 3. Referring to FIG.
5 corresponding to FIG. 2 and showing a section of the topsheet 2,
the lower sheet 8 underlies the upper sheet 7 which is provided
with the skin-contacting area 14 and the liquid passages 13, and
the lower sheet 8 includes the skin-noncontacting area 15 and the
truncated-cone- or cone-shaped exposed area 25 which defines the
space 18A therein. Mutually opposing inner surfaces of the
skin-contacting area 14 and the skin-noncontacting area 15 are
spaced from each other and cooperate with the wall of the
associated liquid passage 13 to form the cavity 20.
FIG. 6 is a magnified microscopic photo of the topsheet 2 showing,
in details, the skin-contacting area 14, the upper openings 11 of
the upper sheet 7 and the apex 18 of the lower sheet 8 as viewed
from obliquely above.
FIG. 7 is a photo of the topsheet 2, magnified as viewed from right
above. As shown, the upper sheet 7 and the apex 18 respectively
comprise the melt-blown fibres, the apex 18 presenting a fibre
distribution density lower than in the upper sheet 7.
FIG. 8 is a magnified photo (50x) of the topsheet 2 in a section
cut in the direction of its thickness, showing the liquid passages
13 and the truncated-cone-shaped exposed area 25 of the lower sheet
8. Though inadequately clear, it will be seen that the wall of
liquid passage 13 is two-layered, i.e., consists of the melt-blown
nonwoven fabrics 7a, 7b; the lower sheet 8 is welded to and/or
twist about the upper sheet 7 around the lower openings 12 of the
liquid passages 13; the V-shaped groove 19 is formed by the side
wall 17 of the exposed area 25 and the adjacent wall of the liquid
passage 13; and the apex 18 of the exposed area 25 is substantially
coplanar with the skin-contacting area 14.
Instead of using the above-mentioned melt-blown nonwoven fabric, it
is also within the scope of the invention to form the upper sheet 7
which is the important component of the topsheet 2 by using the
nonwoven fabric made of other thermoplastic synthetic resin fibres
or thermoplastic synthetic resin sheet. Preferably, the upper sheet
7 is made from suitable hydrophobic material so that a dry touch
may be maintained even after the excretion of body fluids, and the
lower sheet 8 can be formed also from hydrophilic thermoplastic
synthetic resin nonwoven fabric other than the melt-blown nonwoven
fabric so that the body fluids may be transferred toward the
absorbent core and at the same time extensively spread over the
lower sheet 8 as rapidly as possible. Such hydrophilic nonwoven
fabric destined to form the lower sheet 8 may be obtained, for
example, by coating the nonwoven fabric made of polyolefins such as
polyethylene and polypropylene or polyesters with 0.1% aqueous
solution of hydrophilicity giving agent such as fatty acid alkyl
amide cationic agent or by homogeneously mixing any one of said
synthetic resins with 0.3 to 1.0 w % of hydrophilicity giving agent
such as glycerin monostearate and by using this mixture as starting
material for the desired nonwoven fabric.
Instead of using such hydrophilicity giving agent, it is also
possible to employ, as the lower sheet 8, the nonwoven fabric
obtained from starting material as follows: ethylene-- --olefin
copolymer having a density less than 0.900 g/cm.sup.3 and a degree
of crystallinity of 5 to 40% or resinous composition containing
this copolymer as its main ingredient, for example, the ethylene--
--olefin copolymer of 100 parts by weight blended with resin of
parts by weight less than 100 such as low, medium or high density
polyethylene, linear low density polyethylene, polypropylene,
polybutene-1, or ethylene-vinyl acetate copolymer.
A specific example of the ethylene- -olefin copolymer has 3 to 10
carbons in its --olefin, ethylene content of 85 to 95 mol %, melt
flow rate (MFR) of 1 to 200 g/10 min measured under a load of 2160
g at 190.degree. C. (according to ASTM D1238), a density of 0.870
g/cm.sup.3 to 0.900 g/cm.sup.3 and a degree of X-ray crystallinity
of 5 to 40%. The nonwoven fabric such as melt-blown nonwoven fabric
obtained from the above-mentioned resin or resinous composition is
not only hydrophilic but also soft and stretchable, so particularly
suitable for the material of the lower sheet 8. It should be
understood that the ethylene-- --olefin copolymer or the resinous
composition containing this copolymer as its main ingredient or the
sheet of nonwoven fabric or the like obtained therefrom may be
treated with said hydrophilicity giving agent to further enhance
its hydrophilicity.
In the topsheet constructed according to the invention, the liquid
passages are effectively shape-stabilized and difficult to be
blocked, since the lower sheet is welded to and/or twist about the
upper sheet around the lower openings of the respective liquid
passages.
The cavity defined between the upper sheet and the lower sheet
serves to prevent the body fluids from flowing back to the upper
sheet even when the lower sheet is wetted with the body fluids
spreading over the lower sheet, so the absorptive articles
employing this topsheet never give the wearer the unpleasant feel
of wetness.
The body fluids excreted over the topsheet rapidly reach the lower
openings of the liquid passages under the effect of capillary
phenomenon occurring between each pair of the adjacent wall of the
liquid passage and side wall of the exposed area rising up into the
liquid passage, then partly pass through the lower sheet and are
absorbed by the spot of the absorbent core which immediately
underlies the lower opening of this liquid passage, partly spread
over the lower sheet and are absorbed by the remainder portion of
the absorbent core being in contact with the skin-noncontacting
area of the lower sheet. In this manner, the topsheet of the
invention allows the absorption rate to be improved over the
topsheet of prior art merely provided with the liquid passages.
If the apex formed by the portion of the lower sheet rising up into
the liquid passage is composed of hydrophilic nonwoven fabric
adapted to come in contact with the wearer's skin, said capillary
phenomenon serves also to transfer sweat when the wearer is sweaty.
Accordingly, even when the upper sheet is made of hydrophobic
plastic film, the topsheet can be sweat-absorptive. While the apex
may possibly absorb some quantity of moisture from the absorbent
core under the capillary effect, such quantity of moisture absorbed
back can be minimized by the space defined between the apex and the
absorbent core.
High shape-stability of the liquid passages improves a cushioning
effect and therefore comfortableness of wearing the absorptive
articles.
The topsheet can be easily manufactured, since the melt-blown
nonwoven fabric is formed merely by blowing molten fibres against
the underside of the upper sheet.
With the apparatus of the invention for making the topsheet, the
upper sheet is formed by the first and second melt-blow extruders
exclusively used to form the first and second sheets, respectively
and then the lower sheet is formed by blowing molten fibres from
the third melt-blow extruder against the underside of the upper
sheet, thus allowing the topsheet to be continuously produced.
* * * * *